The present invention relates to an alkaline, pulverized active substance for the deacidification of printed matter, wherein the active substance is distributed over the printed matter by means of air and a device for the deacidification of printed matter, in particular, printed matter which can be fanned out, such as bound books, by means of air streams laden with alkaline active substances in a receiver having supporting parts for the insertion of printed matter.
Since the invention of mechanical wood pulp in 1844, all printed matter worldwide has undergone decomposition caused by inherent overacidification. In order to save the cultural wealth stored in billions of documents, numerous experiments have been carried out to deacidify the paper matter.
These experiments can be divided into three groups:
1. Wet treatment
2. Gas treatment
3. Dry treatment with alkaine powder
Wet treatment using solutions such as peroxide, etc. has proved to be the most dangerous method of treating valuable documents; the pages become distorted or curl, and in some cases the ink even dissolves and runs. The use of gases such as morpholine vapours, etc. requires the use of a costly vacuum chamber and also increases the cycle time for the treatment. Dry treatment with alkaline powdered substances has often failed owing to the non-uniform application of the powder and the effectiveness of the substance.
One process for the deacidification of printed matter and a substance is known from U.S. Pat. No. 5,433,827. In this process, the pages of books are brought into contact with paper coated with a highly concentrated deacidifying substance and mechanically compressed for several days at a high level of humidityxe2x80x94over 75%, preferably 97% relative humidity. Alkali carbonates and alkaline-earth carbonates and their mixtures are used as the deacidifying substance. An alternative proposal is to dust with calcium or magnesium carbonate the pages to be deacidified. The processes are based on ionic migration of the deacidifying substance and are therefore largely dependent on pressure and humidity. The processes described are also very labour-intensive and take from one day to several weeks to carry out.
Therefore, the primary object of the invention is to provide a fast reacting active substance for the deacidification of printed matter, in particular also bound books. The quality of the paper should be of secondary importance, i.e. the active substance should be as universally usable as possible. It must not damage or alter the printed matter. The active substance must be applied uniformly over the entire surface of the paper and produce the same pH value from the first to the last page of a book.
A device according to the preamble of claim 6 is known (DE-A1-44 36 635) in which books are held by the spine in a vertically arranged holder and circular-section jets laden with active substances move and blow through the individual pages from the bottom upwards. This results in heavy mechanical loading of the pages, which are also not leafed through in a defined manner, i.e. the diffuse circular-section jets do not uniformly charge the pages with active substance. The device is not suitable for individual pages or plates because the non-uniform application of the active substance has a particularly negative effect.
Accordingly, an improved device is to be provided which is fitted with a receiver and is also able to deacidify bound books, catalogues, brochures, etc. without mechanically impairing or damaging them.
The active substance is distinguished by good adhesion to the surface of the paper and, owing to the residual moisture still present therein, is three-dimensionally distributed over the paper.
The mixture described in claim 2 gives a resulting pH of 9.0 to 9.5, i.e. an alkaline excess is established on the paper, thereby neutralising any further progressing acidification.
An alkaline, pulverized active substance comprising a mixture of at least two dried and organic salts, the anionic parts of the salts having a relatively low acidity constant, in that a salt having relatively low water affinity is the main constituent of the active substance and in that the one further salt has relatively high water affinity wherein the salt having high water affinity is potassium carbonate and the salt having relatively low water affinity is potassium hydrogen carbonate, and wherein the potassium carbonate is present in the active substance in an amount of 7% to 15% by weight and wherein the active substance has an average particle size of 20 micrometers to 30 micrometers and a residual moisture content of less than 20% by weight gives a resulting pH of 9.0 to 9.5, i.e. an alkaline excess is established on the paper, thereby neutralizing any further progressing acidification.
An alkaline, pulverized active substance comprising a mixture of at least two dried and organic salts, the anionic parts of the salts having a relatively low acidity constant, in that a salt having relatively low water affinity is the main constituent of the active substance and in that the one further salt has relatively high water affinity wherein the salt having high water affinity is potassium carbonate and the salt having relatively low water affinity is potassium hydrogen carbonate, and wherein the potassium carbonate is present in the active substance in an amount of 0.1% to 5% by weight and wherein the active substance has an average particle size of 28 micrometers to 35 micrometers and a residual moisture content of less than 15% by weight has proved successful in selectively setting a pH of 8.2 to 8.5 and is used for less stressed documents.
Alternatively, a mixture according to either of the foregoing is used, with the addition of potassium hydrogen phosphate or ammonium thiocyanate is present in the active substance in an amount of 1% to 5% by weight, the resulting pH of which is adjustable in a range from 7.2 to 7.5.
The addition of polystyrene balls increases the flowability and thus the conveyability of the active substance.
Placing the printed matter in the invented device has proved particularly successful, the device leafing through the printed matter and uniformly charging it with active substance by means of a staggered row of flat jets. In the case of bound books, these are inserted into the supporting parts with the spines facing downwards and are gently treated by the device. By means of suitable holding arrangements, however, unbound or non-stitched leaves can also be treated.
Preferably, the receiver for the printed matter is accommodated in a case closable by a hinged cover, thereby avoiding emissions.
The invented device has been found to be advantageous from the point of view of promoting flow when the air diffuser (15) is box-shaped.
It has been found kinematically advantageous, i.e., only reguiring a simple drive, when the aie diffuser (15) of the invented device is arranged in a horizontal plane and is laterally displaceable above the supporting parts (2, 2xe2x80x2).
The invented device has been found to be advantageous from the point of view of promoting flow when the air diffuser (15) is box-shaped.
By the use of a fan, the active substance is circulated and thereby used repeatedly.
By the incorporation of a secondary flow with a filter, the device can be emptied of powder and thus opened without problems.
A dehumidifying chamber, which is inserted into a further secondary flow and by means of which the moistness of the applied powder is kept relatively constant, has proved successful. The moisture drawn out of the books during treatment is thereby absorbed.
The recirculation of the secondary flow into the main flow allows particularly simple control of the humidity inside the device.
Feeding the secondary flow in at the powder inlet is advantageous because in this way the powder is first acted upon by dry air and conveyed before it comes into contact with the moister air of the main flow.
In large installations, a thermal dehumidifying and heating system appears advantageous because it permits virtually continuous operation.
Embodiments of the invention will be further described in the following with reference to drawings, in which like reference numerals are used for like functional components: